The aircraft are provided with numerous instruments aiming notably to limit the risks of accidents. There is a category of accidents designated by the expression Controlled Flight Into Terrain (CFIT). This category includes accidents during which an aircraft that can be flown under the control of its crew unintentionally strikes the relief, obstacles or a sheet of water without the crew being aware of the imminence of the collision.
To limit the risk associated with controlled flight into terrain accidents, new monitoring instruments have been developed. Notable among these is the terrain awareness and warning system. This system notably comprises a topographical database on the relief of the terrains.
However, the terrain awareness and warning systems do not have a function for predicting collisions with obstacles, such as, for example, man-made obstacles like electricity lines or even very high constructions. Needless to say, taking these obstacles into account would make it possible to very significantly improve the surveillance on the ground, particularly in the take-off and landing phases.
Taking obstacles into account in a terrain awareness and warning system comes up against the difficulty of having to potentially deal with a particularly high number of obstacles in certain geographic zones. Furthermore, the accuracy of the topographic data for the obstacles can vary widely from one information source to another, which makes the job of calculating the warnings complex. The multitude of obstacles and the variability of the level of accuracy of the coordinates of an obstacle raises a risk of triggering false alarms prejudicial to keeping the crew correctly informed.